It has been proposed to use polyhydroxyl polyethers with a high ethylene oxide content for producing polyurethane foams and/or to add suitable fillers to the reaction mixture (German Offenlegungsschrift No. 1,127,040). Certain substances which increase the hydrophilic character of the polyurethane foams have also been added to the reaction mixture in order to obtain a foam which may be wetted with water (German Offenlegungsschrift Nos. 1,694,027 or 1,694,028).
Although the methods described above result in a foam which may be wetted with water, the other mechanical properties of the foam are thereby deleteriously affected, in particular the tensile strength and elongation at break. In addition, these foams frequently swell in water. Moreover, the salt compounds which render the foams hydrophilic are relatively easily washed out of the foams so that the water absorption capacity of the foams decreases.
It is important to note that no hydrophilic agents are presently known which may be used for both soft and hard polyurethane foams. Although processes are known by which open-celled hydrophilic polyurethane hard foams may be produced, these processes are inapplicable to soft polyurethane foams, and vice versa.
The process discovered according to the present invention enables the disadvantages described above to be overcome.